The city's share of jobs in the securities industry has hit fresh lows, currently accounting for less than 19% of all U.S. securities industry jobs, according to the latest Labor Department data, well below the 30% share the city boasted two decades ago.

The exodus began in the early 1990s when banks and brokerage firms started moving administrative and back-office workers to lower-cost locales across the Hudson, often in return for hefty tax breaks. The city's Wall Street middle class was hollowed out, but its tax base wasn't harmed because the higher-paying jobs mostly stayed put.

That could be changing, however, because in recent years, cost-conscious banks have begun moving higher-end investment-banking and analyst positions out of town. In July, Deutsche Bank said it would add 300 positions in Jacksonville, Fla., where it currently has about 1,600 staffers, up from just 100 in 2008. In August, Citigroup said it plans to boost its Jacksonville workforce by 20%, or 800 people. Goldman Sachs' Salt Lake City office, which opened in 2000, employs some 2,000.

The fiscal well-being of both the state and city remains closely tethered to the financial industry, despite efforts to diversify the economy by stoking sectors like tech and tourism. Wall Street contributed more than a sixth of the state's tax revenue last year and accounted for more than a fifth of all private-sector wages paid in the city.

Although the securities industry makes up less than 5% of the workforce, the Partnership for New York City estimates that 700,000 jobs in sectors like restaurants and retail depend on financial-services dollars.

Meanwhile, even as New York's big banks beef up elsewhere, their overall head count is falling. Citi has let go of 8% of its staff in the past 12 months, or 19,000 people, while Goldman has eliminated 5% and Morgan Stanley 2%.

But there may be good news on the horizon for New York: the bad news in Britain. The ranks of Wall Streeters could rise as bankers flee London in anticipation of the U.K. exiting the EU. In a conference call last week, Goldman finance chief Harvey Schwartz said, "Brexit potentially is something that could drive share to the U.S."

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